The present invention relates to a die casting apparatus, and more particularly to a die casting apparatus for producing a die casting by supplying molten metal into a die cavity defined by a movable die and a fixed die, the die casting apparatus preventing the molten metal from being oxidized while it is ,being forced into the die cavity, being capable of easily recovering small metal pieces attached to a plunger which forces the molten metal, and also preventing the molten metal from being scattered, so that the produced die casting will be of good quality and no unexpected accidents will occur during the production of the die casting.
As disclosed in Japanese Laid-Open Utility Model Publication No. 59-6055 and Japanese Laid-Open Patent Publication No. 41-10612, conventional die casting apparatus have a feed pipe for feeding molten metal to the die cavity. The feed pipe is connected between the die cavity and a heating furnace which contains molten metal at a desired temperature. By forcing the molten metal under pressure into the feed pipe, the molten metal is forcibly fed into the die cavity, in which the molten metal is forcibly or naturally cooled to produce a die casting.
The feed pipe has its inner wall communicating directly or indirectly with ambient air, so that the ambient air can always flow into and out of the feed pipe. A thin film of molten metal which may be attached to the inner wall of the feed pipe is therefore exposed to ambient air, and combined with oxygen contained in the ambient air thereby forming an oxide, which tends to be deposited on the inner wall of the feed pipe. The oxide deposit on the feed pipe may grow to the extent which clogs or unduly limits the passage in the feed pipe, with the result that molten metal cannot smoothly flow through the feed pipe.
The deposited oxide may come off the inner wall and flow into the die cavity, whereupon a die casting with the oxide mixed therein will be produced. The die casting thus produced is of poor quality and has an insufficient degree of mechanical strength required for a final product. The die casting containing such oxide also lacks a desired degree of uniform density.
Some molten metal is liable to be forced out through a small gap between the outer peripheral portion of the tip end of a plunger which forces the molten metal into the die cavity, and the injection sleeve. The molten metal which has thus been forced out turns into small metal pieces which may contaminate surrounding areas or break other nearby machines and apparatus.